Cochlear blood flow monitoring is essential during neuro-surgical procedures, which may disrupt inner ear blood flow, and also promises to provide important information to determine therapy for Sudden Deafness Syndrome. Laser-Doppler flowmetry has been used in the cochlea, but is surgically difficult to implement, is vulnerable to motion artifact, and observes regional rather than total cochlear blood flow. This proposal is to build a novel high-frequency pulse Doppler ultrasound instrument to detect blood flow in the common modiolar vein (CMV), which comprises venous return for nearly all inner ear blood flow. The device will detect blood flow via the round window niche, which is easily accessible and outside the acoustic neuroma operating field. This instrument will provide immediate benefits in intra- operative monitoring of cochlear blood flow during acoustic neuroma surgery, and as a diagnostic aid for sudden deafness. A prototype will be constructed in Phase I and then tested on guinea pig model of the human CMV. Phase II will include integration of the ultrasound transducer into a catheter which can be secured in the human round window niche, and clinical trial testing. Phase II results will be used to design a Phase III device for the commercial market. PROPOSED COMMERCIAL APPLICATION No proposed commercial appliction given.